Designing a Specialized Voltage Regulator
The purpose of this regulator design is to accommodate generators featuring a higher output voltage, commonly utilized in specific applications like boats and emergency service vehicles. These generators are essentially modified versions of standard car alternators. In these generators, the field winding is connected to the 12 V (or 24 V) battery supply. While the generator winding is tailored for the AC grid voltage (either 230 V or 115 V). The challenge lies in maintaining stability in this AC voltage via the 12 V field winding. Although a switching regulator is a viable option, we deliberately opted for the tried-and-tested 723 regulator for this application.
Unique Generator Configuration
The generator in question operates as a three-phase type, with its field winding designed to handle 12 VDC. The output voltage of the generator varies based on its revolutions and the current flowing through the field winding. This unique configuration necessitates a regulator that can handle the specific demands of this setup, ensuring stable voltage output despite the dynamic nature of the generator’s operation.
Optocoupler-Driven Voltage Regulation
In this setup, where the output voltage is relatively high, it is channeled through optocouplers to the 723 regulator, configured in a standard manner. The regulated output then passes through driver T1 to two parallel-connected 2N3055 transistors. These transistors collectively deliver the necessary current to the field winding, ensuring stable operation.
Optocoupler Selection and Challenges
In the prototype, TLP620 optocouplers were employed, featuring two antiparallel LEDs at the input, making them suitable for alternating voltages. Despite their suitability, there can be variances in sensitivity between the internal LEDs due to manufacturing constraints. To enhance precision, employing two individual optocouplers per phase, with anti-parallel input connections and parallel output connections, offers more accurate regulation. To maintain adequate isolation between the primary and secondary sides, creating a cutout beneath the middle of each optocoupler on the PCB is essential.
Component Choices for Improved Performance
For better precision, replacing the BD136 with alternatives like TIP32 is a viable option for T1. Additionally, opting for transistors with plastic casings for T2 and T3, as opposed to TO3 cases, can enhance the overall performance and stability of the circuit. Careful component selection ensures the circuit’s efficiency and reliability, crucial for its functionality in the specified applications.